sciadv.adk6320

Supplementary Materials for

The largest freshwater odontocete: A South Asian river dolphin relative from

the proto-Amazonia

Aldo Benites-Palomino

et al.

Corresponding author: Gabriel Aguirre-Fernández, gabriel.aguirre@pim.uzh.ch

Sci. Adv.

, eadk6320 (2024)

DOI: 10.1126/sciadv.adk6320

This PDF file includes:

Supplementary Text

Sections S1 to S3

Figs. S1 to S7

Table S1

References

Supplementary Text

S1: Extended geological context

The holotype specimen of

Pebanista

yacuruna

gen. et sp. nov., MUSM 4017, was uncovered

from sediments of the Miocene Pebas Formation exposed along the Napo River in Western

Amazonia of Peru

(lat: -3.012468°, long:

-73.404855°,

Amazon Basin). The unit is associated with

a large-scale continental freshwater aquatic system (fluvio

-lacustrine setting), which was at least

twice affected by short-lasting regional marine floodings sourced from Caribbean marine

waters(

). The Pebas Fm. has an estimated thickness of up to 1000 meters(

). However,

individual sections outcropping along riverbanks in the Amazon Basin rarely exceed a few tens of

meters, making it virtually impossible to determine robust regional correlations and precise ages.

The

Pebanista

locality consists of an 8-meter-thick section, characterized by having massive to

finely laminated blue to brown siltstones, interbedded with brown fine-grained sandstones,

occasional black fossiliferous mudstones, and a massive indurated fossiliferous co

quina level. The

Pebanista

remains and other fossils found at the locality, such as mollusc shells, and bony remains

of a

Purussaurus

caimanine and a sloth, come from this coquina level.

Palynological Biostratigraphy and Biochronological Implications

–During our 2018

fieldwork campaign that yielded the holotype specimen of

Pebanista yacuruna

, we collected

four samples (at 1-meter intervals) for palynological analyses from the section bearing the

holotype. Two samples were located below (RN39-02; RN39-04) and two above (RN38-02;

RN38-03) the stratigraphic position of the fossil specimen. Samples were processed for

palynological analysis following standard digestion procedures by using 10% HCl and 40%

HF(

). Each sample was sieved using 10 μm and 100 μm meshes and permanent montages

were prepared. Light microscopy was used to examine the palynological content, following

morphological features, descriptions, and illustrations compiled in Jaramillo and Rueda

(

). The

section was dated using the palynological zonation proposed by Jaramillo et al.

(

), which has

been time-calibrated using carbon isotopes, radioisotopic dating, foraminiferal biozonations, and

magnetostratigraphic data. A Maximum Likelihood (ML) analysis was then applied to

statistically infer the most probable ages based on taxa abundan

ces(

), while keeping the same

zonation as the biostratigraphic reference. R code and reference datasets were from Ochoa et

al(

Good pollen recovery was found in all samples, being characterized by high abundances of

fern spores (e.g.,

Polypodiisporites

and

Laevigatosporites

) and palms (e.g., Mauritiidites). We

found no evidence of taxa reflecting marine or brackish environments in this section. The co

occurrence of key temporal indicator taxa, such as

Malvacipolloides maristellae

(First Occurrence

Datum or First Appearance Datum [FAD] at 17.7 Ma),

Echitricolporites spinosus

(FAD at 17.1

Ma), with

Cyclusphaera scabrata

(Last Occurrence Datum or Last Appearance Datum [LAD] at

16.9 Ma), and

Crassoretitriletes vanraadshooveni

(FAD at 14.2 Ma), supports the presence of the

Early Miocene zones T-13, T-14 and the lower part of zone T-15 (17.7

-14.2 Ma) in this section.

Furthermore, according to the ML analysis, the studied samples have a high probability of

belonging to the

Early Miocene palynological zone T-13

E. maristellae

, restricting the age of the

Pebanista

section to the upper Burdigalian Stage, circa 16.5 Ma (Supplementary Figure 2)

S2: Extended description of

Pebanista yacuruna

gen. et sp. nov., MUSM 4017

Phylogenetic

position of

Pebanista

–Our series of phylogenetic have consistently recovered

the relationships of

Pebanista

yacuruna

within Platanistidae. In the

first heuristic search, 72 trees

were retained with a length of 105 step, a CI=0.600 and a RI of 0.817.

Pebanista

Platanista

were

recovered as sister to

Zarhachis

Pomatodelphis

; however,

Araeodelphis

was recovered within a

large polytomy that included other platanistoids.

In the series of analyses with implied weighting

the content of Platanistidae was consistent with

previous workers

(

In these analyses with

subsequent k values, 13 trees were retained with a length of 13 steps, a CI=0.600 and a RU=0.817.

Platanistidae was recovered by the following combination of characters:

articular rim on the lateral

surface of the periotic forming a hook-like process

{c. 20(2)},

separate ossicle at the apex of the

anterior process of the periotic

{c. 26(1)},

outer posterior prominence of the tympanic posteriorly

longer than the inner posterior prominence {c.

29(1)}

and mandibular symphysis

reaching

than 65% of the mandibular length, including an angle between both mandibles broader than 50°

{c.

47(1)}.

Araeodelphis

is recovered as the earliest branching platanistid due to a single character:

absence of asymmetry in the rostrum {c.

4(0)}.

The clade formed by the more crownward

platanistids, without

Araeodelphis

is recovered

by apex of the rostrum formed by both premaxillae

and maxillae {c.

2(2)},

deeply grooved lateral rostral suture between the premaxilla and the

maxilla {c.

3(1)},

presence of a distinct prominent dorsal crest in the antorbital

-supraorbital region

{c. 9(1)},

antorbital process of the frontal transversely thickened {c.

10(1)},

lack of accessory

denticles on posterior teeth {c.

33(1)}.

The monophyly of

Pebanista

and

Platanista

is recognised

due to large and thin-edged aperture of the cochlear aqueduct of the periotic {c.

22(1)},

oval

internal auditory meatus of the periotic with the dorsal opening for the facial canal lateral to the

spiral cribriform tract {c.

25(1)},

tooth count between 25 and 33 {c.

34(1)},

vertex strongly

pinched transversely with the posterior end of the maxillae converging posterior to the external

bony nares

{c. 41(1)},

transversely wide temporal fossa

{c. 44(0)}.

Pebanista

differs from

Platanista

by possessing a transversely thickened antorbital process of the frontal, ventral

exposition of the palatines and greatly enlarged alveoli {c. 46 (0)}.

General description of the skull

–The holotype skull of

Pebanista

yacuruna

gen. et sp. nov.,

MUSM 4017, has a preserved condylobasal length of 698 mm and an estimated bizygomatic width

of 281 mm. The preserved skull dimensions are proportionally larger than other Platanistidae

including extant

Platanista

, and the fossil taxa

Araeodelphis,

Pomatodelphis, Prepomatodelphis

and

Zarhachis

. The sutures between the cranial bones are well

-closed or fused (e.g., maxilla-

premaxilla suture along the rostrum) indicating that it belonged to a fully mature specimen. The

rostrum is dorsoventrally flattened and

elongated, a condition shared with

Pomatodelphis,

Prepomatodelphis

and

Zarhachis

, thus contrasting with the transversely compressed rostrum of

Platanista

(

). On the preserved portion, the rostrum is formed by the premaxillae, maxillae,

and vomer, being much more transversely robust than in other platanistids. The rostrum exhibits

several well-preserved dental alveoli which are well

-developed, much larger, and

deeper than in

other platanistids. The facial region of the skull exhibits a well-developed circumnarial basin,

delimited laterally by the supraorbital crest, and posteriorly by the nuchal crest. The external bony

nares are displaced to the left, creating

an asymmetric arrangement of the surrounding bones. Only

the left supraorbital crest is preserved, projecting substantially over the level of the base of the

rostrum and being transversely flattened as in

Platanista

, but more robust. This crest is not as stout

as in

Pomatodelphis

and

Zarhachis

. The medial aspect of the crest is excavated by various

vacuities, a condition also present in

Platanista

, but to a lesser extent in the new fossil taxon. No

excavation of the supraorbital crest is observed in

Zarhachis

and

Pomatodelphis

. The temporal

fossa is transversely longer than high and extends posteriorly, projecting the temporal crest well

into the occipital region. Over the temporal fossa, the nuchal crest continues anteriorly, forming

supraorbital crests and giving the skull a boxy outline in dorsal view. The occipital shield is

perpendicular to the longitudinal axis of the skull, except for its dorsal end, which

deflects

anteriorly. However, it is not possible to assess whether this is the true shape of the crest, or a

condition enhanced by taphonomic compression.

Premaxilla

–Along the rostrum, the

dorsal surface of the

premaxillae

is flat to slightly convex

until the level of the antorbital notch, where the medial part of these deepens forming the

circumnarial basin. Posteriorly, across the facial region of the skull, the premaxillae become

slightly concave medially

forming the premaxillary sac fossae. In dorsal view, the premaxillae are

greatly exposed along the rostrum, limiting the dorsal exposure of the maxillae to a narrow strip

along most of the rostrum. Both premaxillae retain a similar transv

erse width along the rostrum,

without any narrowing or lateral expansion. The maxillary

-premaxillary suture is well-closed and

partly fused, being located within a narrow, shallow groove, much thinner than the condition

observed in other platanistids such

Pomatodelphis

Zarhachis

Platanista,

which exhibit a

deep lateral groove. The mesorostral groove is closed along most of the rostrum, opening

posteriorly at the level of the last maxillary tooth. The anteromedial sulcus is well

-developed on

the left

premaxilla, being narrower on the right premaxilla due to the transverse compression of

the bone, a condition shared with other platanistids and squalodephinids. The single premaxillary

foramen is located on the left premaxilla, 21mm anterior to the level

of the external bony nares,

being longer (15mm) than wide (6mm). As in

Platanista

, this single premaxillary foramen is

located at the level of the antorbital notch, and not anterior to it. The posteromedial sulcus is

slightly narrower than its anteromedial

counterpart, being mostly rectilinear on the left premaxilla

and slightly curved on the right. On the facial region both premaxillae are strongly deflected to the

left side of the skull, thus making the left external bony naris longer than wide and the ri

ght naris

wider than long. Both premaxillae reach their highest elevation posterior to the external bony nares

at the level of their respective nasal processes. The premaxillary sac fossa is well

-developed on

the left premaxilla, having a kidney

-like shape. Because of the transverse compression, the

premaxillary sac fossa on the right exhibits an oval outline.

Maxilla

–The maxillae are mostly restricted to the lateral sides of the rostrum, being flat

across the rostral surface. Anterior to the rostral base, the maxillae slightly project laterally and

flatten, creating a blade-like ending of the maxillary flange, as in o

ther platanistids. Ventrally, the

maxillary surface is

flat, and both maxillae contact each other until the level of the 13

dental

alveolus

(counting from the back), where the vomer is exposed ventrally as a narrow strip. The

widest alveolus has an anteroposterior length of 16mm and a transverse width of 18mm. Posterior

to the maxillary flange, the antorbital notch displays an acute V

-shaped outline. A single dorsal

infraorbital foramen is preserved on the left maxilla, displaying a sub

-elliptical

outline, reaching

an anterodorsal length of 11mm and a transverse width of 4mm. No additional foramina can be

identified within the maxillary surface. In the facial region, both maxillae are highly asymmetric,

due to the deviation of the external bony nare

s, following the pattern of their respective premaxilla.

The lateral region of the ascending process of the maxilla projects dorsolaterally, forming the U

shaped circumnarial basin along with the premaxillae. Such development of the circumnarial basin

is a condition unique to

Pebanista

being a more-derived condition than the one observed in

Platanista

and because of the overall contribution of the premaxillae and maxillae to the structure

it resembles the supracranial basin observed in other odontocetes

(

). Laterally, the

circumnarial basin is surrounded by the greatly enlarged supraorbital crests, which are mostly

formed by the frontals. The maxillae only contribute to a minor part of the medial wall of the

supraorbital crests, at the level of the temporal fossa. Posterior

ly, and within the circumnarial basin

there are two posterolateral depressions located on the floor of the basin, each of which display a

somewhat symmetrical outline.

Frontal + lacrimal

–Most of the left frontal is preserved, except for the dorsal edge of the

supraorbital crest. The right frontal has been lost during the taphonomic process, except for a small

bony strip. The suture between the maxilla and the frontal is mostly fused until

the level of the

temporal fossa, where the suture between both bones can be identified posteriorly. Because of the

shape and the overall development of the circumnarial basin, both frontals should have reached a

similar height and antero

dorsal projection, with minor differences due to the asymmetric profile

of the facial region. In

Pebanista

, the frontals are more enlarged than the condition observed in

other platanistoids, due to the great dorsal development of the supraorbital crests. The frontal is

exposed lateral to the maxillae in dorsal view, displaying a transversely robust profile. In

the

circumnarial basin, the frontal greatly elevates over the rest of the facial region, forming the

supraorbital crest, which is transversely thinner than in

Zarhachis

and

Pomatodelphis

, although

not as thin as in

Platanista

. Furthermore, the dorsomedial region of the crest is excavated by

several large vacuities, which may foreshadow the condition of

Platanista

, in which the medial

aspect of the crest is totally excavated to house a dorsal expansion of the pterygoid sinus

(

). In

dorsal view, the lateral edge of the orbit roof is not parallel to the anteroposterior axis of the skull

as in

Dilophodephis

, but forms an acute angle with the rostrum base, being slightly medially

oriented. In other words, the orbits face anterolaterally. Ventrally, only a small portion of the

lacrimal can be recognised anteriorly contributing to the

preorbital

process. The frontal groove is

moderately broad and shallow, indicating that optic nerve development was limited as compared

Zarhachis

Pomatodelphis

, thus indicating an intermediate condition between these two

genera and the nearly blind

Platanista

Such condition is also reflected by the proportional

reduction in the size of the orbit.

Palatine + pterygoid

–The palatine and pterygoid are not easy to distinguish, as the palatal

in the holotype specimen is compressed and broken into several small bony fragments, and the

palatine-pterygoid suture is fused. In

Pebanista

, the pterygoids have an anterior projection with a

round outline. Medially, the pterygoids contact each other but are not fused. Lateral to pterygoid,

the palatine is ventrally exposed as a small stripe of bone. Most of the medial part of the palatine

has been covered by the pterygoid. As in several platanistoids, the palatine projects dorsolaterally.

Both pterygoid sinus fossae are well-developed, displaying an elongated bean

-like shape,

extending from the level of the antorbital notch to the level of the anterior tip of the s

quamosal.

The hamular process of the pterygoid is mostly missing except for a small area anterior to the

choanae. Posteriorly the pterygoid extends towards the pharyngeal and basioccipital crests,

contributing to most of their preserved length.

Temporal Region

–The skull has undergone a slight to moderate dorsoventral compression

during the taphonomic process, being more evident on the right side of the skull, as the temporal

crest suffers an abrupt break on its posteriormost portion. Despite this, the overall s

hape of the

temporal fossa has been mostly preserved, presenting an oval outline in lateral view, being

transversely broad

and much longer anterodorsally than high. The overall extension of the

temporal fossa in

Pebanista

is much greater than that of

Platanista

Zarhachis

. The fossa projects

into the occipital region, displacing the temporal crest to the occipital region, resembling the

condition in

Zarhachis

Squamosal

–Both squamosals

are partly preserved, each to a similar extent. Only part of the

left zygomatic process is preserved, being much more robust than in

Platanista

, but more slender

than in

Zarhachis

Pomatodelphis

. The supramastoid crest is only noticeable in dorsal view, near

the posterior end of the bone, being broad but not very high. Despite this, the process should have

been moderately robust, based on the broken surface of the squamosal. The glenoid fossa is

small,

with an elliptical outline, and oriented towards the

anterolateral portion of the skull.

Occipital Region

–

Pebanista

displays an occipital region with a trapezoidal outline delimited

by the nuchal crest and the temporal crests. The surface of the occipital shield is mostly

perpendicular to the skull main axis, except for its dorsal part, which projects anteriorly. The

supraoccipital and the posterior end of the maxilla contribute to the anterodorsally oriented nuchal

crest. The foramen magnum and the occipital condyles have been dorsoventrally compressed;

despite this, the overall shape of the surrounding bones indicates that the foramen should have had

a mostly circular outline. The occipital condyles protrude markedly posteriorly, having a rounded

to triangular shape in posterior view.

S3: Description of additional referred specimens

cf.

Pebanista

Referred specimen

– MUSM 3593, an isolated rostral fragment.

Locality, Age and Horizon

–

This specimen was donated by Juan Pablo de Molina in 2018,

and was recovered from the Fitzcarrald Arch, an area in South Central Peru where the middle

Miocene Ipururo Fm. crops out. Despite not having a well

-defined locality, the sediments attached

to the rostral fragment indicate that it corresponds to the fluvial or tidal deposits in this area.

Previous work in the area indicates that the Fitzcarrald Arch was a highly diverse region during

the middle Miocene, as a wide array of taxa including, but not r

estricted to, crocodilians,

cingulates, folivores, astrapotheres, notoungulates, litopterns, rodents, odontocetes and a possible

marsupial have been reported so far(

Description

–

The rostral fragment is rather robust and reaches a maximum length of 13.5 cm

and a maximum width of 8.8 cm, including the premaxillae, maxillae, and vomer. In dorsal view,

the maxilla is restricted to a narrow strip lateral to its respective premaxilla.

Medially the suture

between both premaxillae is somewhat noticeable, being slightly deviated to the left side. The

premaxilla-maxilla suture is located within a narrow, moderately shallow recess, like the condition

observed in the holotype skull of

Pebanista

. The lateral walls of the rostrum are parallel, except

for a minor distortion resulting from to the taphonomic process. Ventrally, both maxillae preserve

four well-developed dental alveoli on each side, with the broken teeth preserved in situ within

these

alveoli. The posteriormost right alveolus reaches an anterodorsal length of 2.9 cm and a

transverse width of 1.9 cm. Only two greatly enlarged teeth are preserved on the left maxilla. The

largest one reaches a 2.4 cm exposure of the crown an

d displays several longitudinal

ornamentations on the crown. The tooth resembles that of

Platanista

, but proportionally much

larger in this fossil. Medially, the vomer is exposed as a narrow strip between both maxillae.

Platanistidae indet.

Referred specimen

– MUSM 4759, isolated tympanic.

Locality, Age and Horizon

–

The isolated tympanic was found in coquina layers of the

lower

Pebas Fm. (Early to Middle Miocene) along the Napo River.

Description

–

The isolated tympanic reaches a maximum length of 5.9 cm, being

anteroposterioly longer than wide, and resembles in general shape that of other platanistoids such

Platanista, Pomatodelphis

Notocetus

(

). In MUSM 4759 the anterior spine is long, but

its overall extension cannot be assessed, as the distal tip is missing. Only the base of the

anterodorsal crest is preserved, as the tympanic plate has only been partly preserved. The

involucrum is well-developed, being rather robust due to the pachyosteosclerotic growth of the

bone. The outer lip exhibits a minor extension anteriorly, similar to the condition observed in

Zarhachis

Platanista

. The preserved portion of the outer lip displays a moderately infl

ated

outline, interrupted by the thin and shallow lateral furrow. Posteriorly, the outer posterior

prominence has a moderately triangular profile

in ventral view, contrasting with the inner posterior

prominence, which displays a much rounder profile. The interprominential notch is wide and

moderately shallow, along with the median furrow which extends across most of the

ventral

surface of the tympanic.

Fig. S1.

Geographical context.

Map indicating the locality where the holotype specimen of

Pebanista

yacuruna

gen. et sp. nov., MUSM 4017, was found (A) and photos from the collection

of the specimen (B, C) along the banks of the Napo River.

Fig. S2.

Stratigraphic ML age

estimates for the MUSM 4017-bearing section, calculated

using a probabilistic approach based on the taxa abundances

. Normalized likelihood values

are represented by color, with higher and lower likelihood values symbolized by warmer and

colder colors, respectively. The lower horizontal axis shows geologic time (Ma), and vertical axis

represents stratigraphic position of specific samples and the upper horizontal axis marks the

palynological zones proposed by Jaramillo et al.

(

Fig. S3.

Holotype skull of

Pebanista

yacuruna

gen. et sp. nov. (MUSM 4017).

Photograph (top),

drawing (middle), and surface (bottom) 3D model in dorsal view.

Fig. S4. Holotype skull of

Pebanista yacuruna

gen. et sp. nov. (MUSM 4017).

Photograph

(top), drawing (middle), and surface (bottom) 3D model in ventral view.

Fig. S5.

Holotype skull of

Pebanista

yacuruna

gen. et sp. nov. (MUSM 4017).

Photograph (top),

drawing (middle), and surface (bottom) 3D model in

left lateral view.

Fig. S6. Additional specimens

cf.

Pebanista

MUSM 3593

rostral fragment in ventral (A,B),

dorsal (C,D) and

right lateral (E, F) views;

Platanistidae indet.

MUSM 4017 isolated tympanic in

dorsal (G,H), ventral (I, J) and lateral (K, L) views.

Fig. S7.

Phylogenetic relationships of

Pebanista

yacuruna

gen. et sp. nov. (MUSM 4017)

Related to Figure 2.

Strict (a) and Adams (b) consensus trees of the heuristic search without

downweighting of characters; and with down-weighting (c,d) homoplastic characters (k=2),

indicating the relationships of

Pebanista

yacuruna

gen. et sp. nov. (MUSM 4017) to other

platanistoids.

Table S1. Cranial measurements (e, estimate; + measurement on incomplete element)

of the

holotype skull of

Pebanista yacuruna

gen. et sp. nov., MUSM 4017 (in mm)

Dimensions

MUSM 4017

Condylobasal length (preserved)

698+

Length of the rostrum (preserved)

489+

Width of rostrum at base

116

Width of the rostrum at 60mm anterior to the line across hindmost

limits of antorbital notches

102

Width of rostrum at mid

preserved

length

Width of premaxillae at mid

preserved

length of the rostrum

Width of rostrum at 3⁄4

of the preserved

length, measured from

posterior end (taken on preserved portion)

Height of rostrum at base (including rostral basin)

Height of rostrum at base (without rostral basin)

Height of rostrum at mid preserved length

Maximum width of the external right bony naris

Maximum width of the external left bony naris

Greatest postorbital width (width across postorbital processes)

261

Minor width within the

supraorbital

processes

115

Maximum width of external nares

Greatest width across zygomatic processes of squamosal

281e

Greatest width of premaxillae

Width across both the temporal fossae

(minimum)

131

Greatest width between lateral margins of exoccipitals

242e

Dorsoventral length of temporal fossa

Anteroposterior

width of temporal fossa perpendicular to greatest

length (dorsoventral height)

124

Length of left orbit from apex of preorbital process of frontal to apex

of postorbital process

54+

Length of antorbital process of left lacrimal

taken horizontally

17e

Greatest width of internal nares

Greatest length of pterygoid

134

Maximum width across occipital condyles

Height of foramen magnum

21e

Width of foramen magnum

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